The present invention relates to a thin film transistor and, more particularly, to a thin film transistor to be used in a liquid crystal display circuit of active matrix type.
The liquid crystal display circuit of active matrix type is equipped with nonlinear elements (e.g., switching elements) individually corresponding to a plurality of pixel electrodes arrayed in a matrix form. Since the liquid crystal in each pixel is theoretically driven (at a duty ratio of 1.0) at all times, the time sharing drive method is adopted. As compared with the so-called "simple matrix method", the active method has an excellent contrast and is becoming a technology indispensable in the color field. The switching elements are represented by thin film transistors (TFT).
In the thin film transistor (disclosed in Japanese Patent Laid-Open No. 35421/1989) used in the conventional liquid crystal circuit of active matrix type, a gate electrode made of aluminum (A1) is formed over a glass substrate, and an anodized film (Ta.sub.2 O.sub.5) of tantalum is sandwiched between a gate insulating film formed over the gate electrode and the gate electrode.
In this thin film transistor, however, the adhesion of the aluminum to the glass is not satisfactory, and the gate electrode may be damaged. Since, moreover, the breakdown voltage of the anodized film of the tantalum is low, the gate electrode and the source electrode or the drain electrode may be shorted.